This invention generally relates to a piston assembly for a standard compressor, and more particularly to a piston assembly with a hard joint having a thermal-insulating barrier for reducing the temperature of the piston sleeve and the cup seal of the compressor hence increasing the life of the cup seal and the compressor.
A typical piston assembly consists of a compressor head connected to a valve plate; a piston sleeve connected to the valve plate and pressure sealed with the valve plate by an o-ring; and a piston which travels inside the piston sleeve. The cup seal, which extends from the midsection of the piston, frictionally engages the interior of the piston sleeve in order to provide a seal between the pressurized and non-pressurized sides of the piston. The cup seal flexes during the upstroke and downstroke of the piston and the frictional engagement creates wear along the cup seal. The act of compression generates heat in the compressor head, which conducts from the compressor head to the piston sleeve via the valve plate. Heat then conducts from the piston sleeve to the cup seal which further hastens failure of the flexible cup seal, limiting the life of the compressor. Reduction of the temperature of the cup seal extends its life, and ultimately extends the life of the compressor.
The valve plate and the piston sleeve connect on the pressurized side of the piston, so a pressure seal must be formed between them to prevent gas leaks. This pressure seal is generally formed between the valve plate and the piston sleeve by an o-ring, which is typically made out of a flexible material. The o-ring is not intended to inhibit heat conduction from the compressor head through the valve plate to the piston sleeve, but merely provides a pressurized seal.
In certain piston assembly designs known as a soft joint assembly, the o-ring, which forms the pressure seal between the valve plate and the piston sleeve, is seated in a groove in the valve plate and the top face of the piston sleeve contacts the o-ring. The contact between the piston sleeve and the o-ring, and the valve plate and the o-ring, are unstable due to the mating of the flat surfaces of the valve plate and piston sleeve with the flexible, round surface of the o-ring. Additionally movement of the piston also causes metal-to-metal contact between the valve plate and the piston sleeve, allowing heat conduction from the compressor head through the valve plate to the piston sleeve. Furthermore, with a soft joint assembly, the clearance volume between the top of the piston and the valve plate when the top of the piston is at dead center fluctuates due to the compressionable nature of the o-ring which effects the compressor's efficiency. While the compressionable nature of the o-ring effects the compressor's efficiency, the compressability is required to ensure a pressure seal between the piston sleeve and valve plate.
In another piston assembly design known as a hard joint assembly, the piston sleeve is seated directly into a groove in the valve plate, creating a metal-to-metal contact point. In this design, the o-ring is located on the outer surface of the piston sleeve to create the pressure seal with the valve plate. An advantage of the hard joint assembly is the fixed clearance volume between the top of the piston and the valve plate when the piston is at top dead center. Since no o-ring is in the assembly, it is easy to control the clearance volume and the repeatability of the compressors' efficiency can be had by controlling the height of the piston sleeve and the clearance volume. However, heat is readily conducted through the metal-to-metal contact of the piston sleeve and the valve plate, resulting in heating of the piston sleeve and ultimately heating and failure of the cup seal.
Thus the known standard compressor piston assembly designs do not inhibit heat flow from the valve plate to the piston sleeve and provide for consistent compressor performance.
Accordingly, it is an object of the present invention to reduce the temperature of the piston sleeve caused by heat conduction from the compressor head through the valve plate to the piston sleeve;
Furthermore it is an object of the present invention to reduce the temperature of the piston sleeve by providing a thermal-insulating barrier between the valve plate and the piston sleeve;
Additionally it is an object of the present invention to provide a durable piston assembly containing a hard joint seal between the valve plate and the piston sleeve having a thermal-insulating barrier between the valve plate and the piston sleeve;
Furthermore it is an object of the invention to reduce the temperature of a piston sleeve by forced air convective cooling.